基于石英增强光声光谱的痕量气体实时检测研究

石英增强光声光谱技术(QEPAS)出现时间较晚，是一种较为新颖的痕量气体探测手段，本文以大气中的水汽作为测量目标，开展对基于QEPAS技术的痕量气体探测系统的研究。理论上，首先对激光器波长调制及信号谐波探测的原理进行了分析，得到了可用于气体浓度信号反演及激光器波长锁定的实现方案，并讨论了可用于高灵敏度气体探测的吸收谱线的选择原则。实验中，以输出波长为1.39 μm的连续波分布反馈单纵模二极管激光器作为激发光源，采用激光器波长调制和2次谐波探测技术，首先研究了激光波长调制深度对QEPAS系统产生的信号幅度的影响，接下来对声波探测系统中微共振腔强声波增强特性进行了研究。QEPAS系统经过优化后，获得了5.9 ppm的探测极限，同时对不同浓度的水汽进行了测量，实验数据线性拟合后，得到R-Square为0.98，证明了此QEPAS系统具有良好的线性响应度。最后，运用基于3次谐波探测的激光器波长锁定技术，对大气中的水汽变化进行了长达12 h的连续测量，实验结果表明，该系统性能稳定，具有良好的连续测量能力，可广泛应用于其他痕量气体的高灵敏度连续在线测量的研究上。

Research on Real-Time Trace Gas Detection System Based on QEPAS

Quartz-enhanced photoacoustic spectroscopy (QEPAS) technology was invented lately. Therefore it’s an innovative method for trace gas detection compared with other existed technologies. In this paper, we studied the trace gas detection system based on QEPAS, and the atmospheric H₂O was selected as the target analyte. In theory, the principles of laser wavelength modulation and signal harmonic detection were analyzed firstly, and the realizing solutions for the gas concentration retrieving and laser wavelength locking were obtained. Furthermore, the selection principle of absorption line for high sensitivity gas detection was discussed. In experiments, a continuous-wave distributed feedback(DFB) single mode diode laser emitting at 1.39 μm was used as the exciting source for the H₂O vapor measurement. Using wavelength modulation spectroscopy and 2nd harmonic detection, the influence of laser wavelength modulation depth on QEPAS signal level was investigated, and the acoustic wave enhancement of the addition of micro-resonator in the acoustic detection module was analyzed as well. After optimization of the QEPAS system, a detection limit of 5.9 ppm for H₂O vapor was obtained. We measured the H₂O vapor with different concentrations, and the R-Square of 0.98 was achieved after the experimental data was linear fitted, indicated that the QEPAS system had an excellent linear response ability. Finally, continuous monitoring of atmospheric H₂O concentration levels for a period of 12 hours was performed when the line locking mode was employed with the help of 3rd harmonic detection. The experimental results showed that this QEPAS scheme had a stable performance and outstanding continuous measuring capacity, and it can be widely used in high sensitivity on-line measurement for other trace gases detection fields.